Exhaust gas recirculation valve with integral feedback proportional to volumetric flow

ABSTRACT

A control valve for an EGR system employs a variable pressure actuator connected to a valve for metering EGR flow and a differential pressure valve connected to supply actuation pressure to the actuator. The differential pressure valve incorporates a proportional solenoid connected to a pressure balancing piston which receives EGR pressure on one side and exhaust flow pressure on the other. The piston is connected to a shaft having an orifice positionable adjacent a pressure source in a first position and a pressure vent in a second position, an outlet of the orifice communicating with the pressure actuator. EGR control is accomplished by providing a signal to the proportional solenoid which shifts the pressure balance point for the piston.

CROSS REFERENCE TO THE RELATED APPLICATION

This application claims the benefit of the filing date of provisionalapplication 60/039,246 having a filing date of Mar. 3, 1997 entitledExhaust Gas Recirculation System Employing A Turbocharger IncorporatingAn Integral Pump, A Control Valve And A Mixer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related generally to the field of internalcombustion engine exhaust gas recirculation (EGR) for emissionsimprovement. More particularly, the invention provides a control valvefor metering exhaust gas to be recirculated for combination with aturbocharger having a compressor wheel with impeller vanes mounted on aside opposite the compressor impeller to act as an EGR pump with aseparate diffuser and volute for EGR flow output from the pump and aseparate scroll inlet to the EGR pump and a mixer for entraining therecirculated exhaust gas in the charge air for the engine.

2. Description of the Related Art

EGR is a known method for reducing the NOX emissions in internalcombustion engines. For effective use, an EGR system must overcome theadverse pressure gradient created by a positive pressure gradient acrossthe engine which is typical of modern high efficiency diesel engines inat least a portion of their operating range. Various approaches toimplementing EGR have included pumping of a portion of the exhaust gasfrom the exhaust manifold to the intake manifold. Pumping has beenaccomplished by introducing the exhaust gas into the compression inletof a conventional turbocharger or supercharger present on the engine or,alternatively, providing a separate compressor receiving the exhaust gasand pressurizing it to a suitable pressure for insertion into the chargeair downstream of the charge air boosting system on the engine. Somefuel consumption penalty is generally incurred by these systems.

EGR also requires adequate mixing of recirculated exhaust gas with theincoming fresh air charge to avoid performance degradation and tominimize mixing losses to avoid additional fuel consumption penalties.Further, positive control of the recirculated exhaust gas flow isrequired to assure proper proportions in the charge air mixture suppliedto the engine intake manifold under varying operating conditions.Additionally, the components and features of an EGR system must beaccommodated within the constraints of limited volume available forallocation in modern engine compartments.

It is, therefore, desirable to provide a highly integrated EGR systememploying pumping components for recirculation of exhaust gas in closephysical and functional cooperation with existing engine systemcomponents such as turbochargers. It is further desirable to configurean EGR flow path and provide novel control components to allow necessarycontrol over exhaust gas flow rates and mixing into the charge air foraspiration by the engine to minimize variation of the percentage ofexhaust gas from cylinder to cylinder.

SUMMARY OF THE INVENTION

A control valve for an EGR system for an internal combustion engineincorporates an EGR valve having a variable pressure actuator foroperating a valve poppet to meter EGR flow from an exhaust flow line toan EGR flow line. The pressure actuator has a pressure port and isresponsive to the pressure in the pressure port. A differential pressurecontroller is attached to the EGR valve and has a first pressure portconnected to the exhaust flow line and a second pressure port connectedto the EGR flow line. A proportional electrical solenoid is connected toa piston in a cylinder forming a first chamber on a first side of thepiston communicating with the first pressure port and a second chamberon a second side of the piston communicating with the second pressureport. The piston is further connected to a shaft supporting a movableorifice with an inlet positioned adjacent a pressure source in a firstposition of the piston induced by lower pressure in the first pressureport than the second pressure port and the inlet of the orificepositioned adjacent a pressure vent in a second position of the pistoninduced by higher pressure in the first pressure port than the secondpressure port. An outlet of the orifice is connected to the actuatorpressure port. Control of the EGR flow is accomplished by providing acontrol signal to the proportional electrical solenoid.

BRIEF DESCRIPTION OF THE DRAWINGS

The details and features of the present invention will be more clearlyunderstood with respect to the detailed description and drawings inwhich:

FIG. 1 is a schematic diagram of an engine and EGR system employing thecombination and components of the present invention;

FIG. 2 is a detailed section view of an EGR pump employed in anembodiment of the invention which is integral with a turbocharger;

FIG. 3 is a detailed section view of a mixer for recirculated exhaustgas from the EGR pump and fresh charge air from the turbochargercompressor incorporated in the disclosed embodiment of the presentinvention;

FIG. 4 is a detailed section view of a valve used in the embodiment ofthe invention shown in the drawings for control of exhaust gas to berecirculated; and

FIG. 5 is a schematic diagram of the operation and elements of the valveof FIG. 4.

FIG. 6 is a detailed section view of a second embodiment of the mixer ofFIG.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings, FIG. 1 shows an internal combustion engine 10having an intake manifold 12 and an exhaust manifold 14. A turbocharger16 is provided for charge air boost, receiving intake air forcompression by a compressor rotor 18 which provides the pressurized airto a charge air cooler 20 prior to introduction into the intakemanifold. The compressor rotor is driven by a shaft 22 connected to aturbine 24 receiving exhaust gas from the exhaust manifold of theengine.

Exhaust gas for recirculation is diverted from the flow out of theexhaust manifold through a control valve 26 to an EGR cooler 28. Gasfrom the EGR cooler is provided to the inlet of an EGR pump which, forthe embodiment shown in the drawings, is a compressor rotor 30 mountedto the turbocharger shaft to be driven by the turbine. The pressurizedexhaust gas from the EGR pump flows to a mixer 32 which combines therecirculated exhaust flow with the charge air to create a substantiallyhomogenous flow stream for introduction into the intake manifold.

FIG. 2 shows the details of a turbocharger employing an integral EGRcompressor according to the present invention. The turbine is containedin a cast turbine housing 34 which incorporates a radial exhaust gasinlet 36 feeding a bifurcated volute 38, for the embodiment shown in thedrawings. Gas flowing through the turbine exits at turbine outlet 40.Shaft 22 is supported by a bearing system including journal bearings 42separated by spacer 44 and thrust collar 46 with bearing 48 all carriedwithin a center housing 50 which incorporates lubrication channels 52.The charge air compressor is contained within a cast compressor housing54 which provides an air inlet 56, a diffuser 58 and a volute 60 for thecompressed charge air.

The EGR pump is incorporated into the existing rotor group of theturbocharger by adding impeller vanes 62 to the backside of thecompressor wheel. A scroll inlet 64 provides exhaust gas forrecirculation and a separate diffuser 66 carries the pressurized exhaustgas to a volute 68. The EGR pump inlet, diffuser and volute areincorporated in a casting 70 which replaces the conventional compressorback plate for the turbocharger, thereby requiring only a small increasein the length of the rotor group and turbocharger as a whole.Segregation of the charge air flow in the compressor and therecirculated exhaust gas in the EGR pump is maintained by a baffle 72which is constrained between the compressor housing and EGR pumpcasting. The EGR pump casting is mounted to the compressor housing usinga retaining ring 74 and bolts 76 received in the compressor housing.

Pressurized exhaust gas from the EGR pump and pressurized charge airfrom the turbocharger compressor and charge air cooler are combined inmixer 32 which is shown in detail in FIG. 3. Exhaust gas from the pumpis introduced to the mixer through an inlet 78 to a volute 80circumferentially distributed about the main fresh air flow pathentering through inlet 82 from the charge air cooler. The voluteintroduces the exhaust gas uniformly about the circumference of thefresh air flow path through slot 84 which has a tailored upstream lip 86of relatively smaller diameter and a downstream lip 88 of relativelylarger diameter to produce a three dimensional angle for the EGR flow topromote both penetration into the core flow stream and a swirl tofurther mix the flow downstream.

The inner wall 90 of the fresh air flow passage is shaped to provide aconvergent/divergent nozzle effect which increases the velocity of thefresh air charge, reduces the static pressure of the flow and enhancesthe entrainment of EGR into the fresh air charge. The mixed flow exitsthrough outlet 92.

A second embodiment of the mixer is shown in FIG. 6 which incorporates adiverging nozzle section 91 to further enhance mixing of the EGR andfresh air charge and enhance velocity matching in the flow.

FIG. 1 shows the mixer as a separate component placed near the intakemanifold inlet. However, placement of the mixer varies in alternativeembodiments and where an EGR cooler is employed, the mixer is locatednear or integrated into the charge air cooler outlet or as a cast ormachined portion of the intake manifold of the engine. In applicationswhere an EGR cooler is not employed, the mixer is located near orincorporated as an integral portion of the compressor housing outlet orthe charge air cooler inlet.

Exhaust gas for recirculation is provided to the EGR pump throughcontrol valve 26. FIGS. 4 and 5 describe the mechanical configurationand operation of one embodiment of the valve. A proportional electricalsolenoid 94 acts on a three-way pneumatic or hydraulic valve 96 withopposing force provided by a piston or diaphragm 97 which is, in turn,acted on by a differential pressure generated by the flow through aseparate exhaust gas recirculation valve 98. The differential pressureis sensed through ports 100 and 102. The three way valve provides supplyair from line 104 to an actuator 106 for the EGR valve or vents actuatorair through vent 108. When the electrical solenoid force is exactlybalanced by the force of the piston, no flow occurs to or from the EGRvalve actuator. When the force of the piston is not sufficient tobalance the force of the solenoid, the three-way valve opens to supplyair to the actuator, thus increasing the EGR flow from the primaryexhaust flow line 110 through the EGR valve into the EGR flow line 112and thus increasing the differential pressure across the valve,restoring the balance of forces. Conversely, when the force of thepiston is greater than the force of the solenoid, the three-way valveopens to vent air from the EGR valve actuator, thus decreasing the EGRflow and the differential pressure across the valve, again restoring thebalance of forces. Control of the amount of EGR is then accomplished byproviding a control signal to the proportional electrical solenoid fromthe engine control system.

As shown in FIG. 4, the EGR valve actuator, for the embodiment shown inthe drawings, employs a diaphragm 114 and spring 116 enclosed in apressure case 118, which position a shaft 120 for controlling valvepoppet 122 on seat 124 to meter EGR flow. The three way valve employs amulti port body 126 incorporating the supply and vent lines with amovable orifice 128 supported on a shaft 130 engaging the solenoid andpiston. A centering spring 132 balances reaction forces of the solenoidand pressure piston.

Having now described the invention in detail as required by the patentstatutes, those skilled in the art will recognize modifications andsubstitutions to the specific embodiments disclosed herein. Suchmodifications and substitutions are within the scope and intent of thepresent invention as defined in the following claims.

What is claimed is:
 1. A control valve for an EGR system for an internalcombustion engine comprising:an EGR valve having a variable pressureactuator for operating a valve poppet to meter EGR flow from an exhaustflow line to an EGR flow line, the pressure actuator having a pressureport, the pressure actuator responsive to pressure in the pressure port;a differential pressure controller havinga first pressure port connectedto the exhaust flow line and a second pressure port connected to the EGRflow line, a proportional electrical solenoid connected to a piston in acylinder forming a first chamber on a first side of the pistoncommunicating with the first pressure port and a second chamber on asecond side of the piston communicating with the second pressure port, ashaft connected to the piston and containing an orifice, the shaftmovable with the piston to position an inlet of the orifice adjacent apressure source in a first position of the piston induced by lowerpressure in the first pressure port than the second pressure port andthe inlet of said orifice positioned adjacent a pressure vent in asecond position of the piston induced by higher pressure in the firstpressure port than the second pressure port, an outlet of said orificeconnected to the variable pressure actuator pressure port; meansconnected to the shaft for balancing the electrical solenoid and piston;and means for providing a control signal to the proportional electricalsolenoid.
 2. A control valve for an EGR system as defined in claim 1wherein the balancing means comprises a spring attached to the shaft.